Ocean sunfish

The ocean sunfish is a fish you catch in the sea. Look for a very large, finned shadow. In the northern hemisphere look for it in Jul – Sep, from 4 AM – 9 PM. It can only appear after you have caught 20 fish. Nook's Cranny pays 4,000 Bells, C.J. pays 6,000 Bells.

A fin shadow in the sea from 4am to 9pm, after 20 catches, worth 4,000 Bells. Between 9am and 4pm a fin can only be this, a whale shark or a suckerfish.